Separation Section H2O and CO2 Removal

The outlet methanation stream contains a high percentage of water and carbon dioxide that need to be removed in order to obtain a concentrated CH4 stream. In the CHEMCAD simulation the stream leaving the methanation section enters into a multipurpose flash unit operating at constant pressure (P = 30 bar) and ambient temperature T = 25°C), where water removal takes place by condensation. 

On the other hand, CO2 is removed by an SCDS column, where the number of stages has been set to 20 and the feeding solvent flow rate to 8 kmol/h at T= 10°C and P = 30 bar. Selexol process for dynamic absorption/desorption (already implemented in the CHEMCAD library) has been selected to perform this step. 

Methane exits from the system in a compressed form and is available for different uses and further conversions. Obtained upgraded concentrations are discussed in the following section, where the methanation unit is presented. 

8 Methanation Section Case 1 Adiabatic Fixed Bed with Intermediate Cooling 

and compressed syngas enters the first methanation reactor (11) at P=30 atm and T = 300°C the stream exiting the methanation reactors (11 and 13) is cooled down (heat exchangers 12-14) in order to lower the temperature of the gas entering the subsequent reactor. The inlet and outlet temperatures and stream compositions for reactors 11,13, and 15 are reported in Table 8.6, for stfeam n and EREA reactor thermodynamics. 

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